[TIR] Fix the error example in the documentation for pad_einsum

[HongHongHongL]

In the documentation for pad_einsum, the example uses

sch.pad_einsum(block, [0, 1, 1])

However, it will cause

Error message: The padding for the block tir.Block#0 are invalid. It should be a list of 3 positive integers.

On a block with trivial binding, this primitive pads the iteration domain of the block by the given padding factors, for example, 127 -> 128, 132 -> 144 when padding factor is 16. So the example should be

sch.pad_einsum(block, [padding factor, padding factor, padding factor])